Laila Kjærbæk, Hans Basbøll
[email protected], [email protected] University of Southern Denmark
Abstract. On the basis of extensive literature studies, Ambridge, Kidd, Rowland and Theakston (2015) present five theses on frequency effects on language acquisition: i) the Levels and Kinds Thesis argues that frequency effects exist at all levels and are of many different kinds (e.g., type and token frequency effects as well as absolute and relative frequency effects); ii) the Age of Acquisition Thesis argues that all other things being equal, frequent forms will be acquired before less frequent forms. Since all other things are not equal, this claim does not entail a one-to-one relationship between frequency and age of acquisition; iii) the Prevent Error Thesis argues that high-frequency forms prevent (or reduce) errors in contexts in which they are the target; iv) the Cause Error Thesis argues that high-frequency forms also cause errors in contexts in which a competing, related lower-frequency form is the target; and v) the Interaction Thesis argues that frequency effects will interact with other effects. The acquisition of the Danish noun plural system is particularly interesting in this regard. The reason is that whereas English is characterized by having one default inflectional marker for a grammatical category (e.g., the plural suffix -s) and a minor number of exceptions to this default rule, Danish has several competing inflectional markers. Furthermore, there are important interactions between phonology and morphology in the Danish system (Kjærbæk, dePont Christensen, & Basbøll, 2014). In this study we will test the theses in a phonological perspective and explore the impact of phonetics on grammar. This we will do in three types of empirical data from children acquiring Danish as their first language: i) Naturalistic data consisting of spontaneous child language input and output from six children between the ages of 0;10-3;11, and their parents; ii) Semi-naturalistic data from structured interviews with 80 children between the ages of 3-9 years; iii) Experimental data from a picture based elicitation task with 160 children between the ages of 3-10 years. We present a scale with three degrees of transparency of the plural stem and of the plural suffix as well as a scale with six degrees of transparency of the Danish plural markers. We furthermore present a scale with three degrees of productivity. Productivity is here defined as the ability of an inflectional marker to occur on new words. For the plural system this means the ability to add the plural marker (stem change + suffix) to a new noun in order to form a new plural noun. We analyze the relation between acquisition rate and degree of transparency as well as degree of productivity.
Keywords: Danish, first language acquisition, frequency, morphology, noun plural, productivity, transparency
Introduction
A review article by Ambridge, Kidd, Rowland and Theakston (2015) presents evidence for the claim that input frequency effects are pervasive in children’s first language acquisition. On the basis of extensive literature studies, they present five theses on frequency effects on language acquisition including considerable empirical support that exists for each of their theses across four domains, namely: 1) single words; 2) inflectional morphology; 3) simple syntactic constructions; and 4) more advanced constructions. The focus of the present study will be on inflectional morphology. Ambridge et al. (2015) argue for a learning mechanism that is frequency sensitive – a claim which is really not that controversial at all, since it is well known that frequency affects language acquisition one way or the other (e.g., Diessel, 2015; Rowe, 2015). Studies of frequency effects are still interesting though, because they reveal something about the learning mechanism and units used in language learning. The interesting question is, however, how frequency interacts with other factors, and this will be the topic of the present study.
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Theses on frequency effects
The five theses presented by Ambridge et al. (2015) are:
1) Levels and Kinds Thesis. Frequency effects exist at all levels and are of many different kinds (e.g., type and token frequency effects as well as absolute and relative frequency effects).
2) Age of Acquisition Thesis. All other things being equal, frequent forms will be acquired before less-frequent forms. Since all other things are not equal, this claim does not entail a one-one relationship between frequency and age of acquisition.
3) Prevent Error Thesis. High-frequency forms prevent (or reduce) errors in contexts in which they are the target.
4) Cause Error Thesis. High-frequency forms, on the other hand, also cause errors in contexts in which a competing related lower-frequency form is the target.
5) Interaction Thesis. Frequency effects will interact with other effects.
We have studied whether Danish children’s acquisition of the noun plural category supports these five theses, and we find the last thesis particularly interesting since the patterning of these interactions can bring us new information on the nature of the learning mechanism.
Factors affecting the acquisition of plural morphology
Earlier studies indicate that (among others) the following factors play a role in the acquisition of plural morphology, confer the Interaction Thesis:
Frequency
It is well known that frequency plays a role in many domains of human development – also in first language acquisition (e.g., Ambridge et al., 2015; Kjærbæk, 2013, 2015; Kjærbæk, dePont Christensen, & Basbøll, 2014). When we refer to frequency in this article, we mean input frequency, though studies indicate that children show effects of output frequency as well. We refer to both token frequency and type frequency (here defined as number of different lemmas).
Transparency
Transparency concerns the extent to which a plural pattern is parsable into its basic units. In English, for example, the plural form hands (hand+s) is more transparent than feet (e.g., Albirini, 2015).
Basbøll, Kjærbæk, and Lambertsen (2011) and Laaha, Kjærbæk, Basbøll, and Dressler (2011) present a typologically relevant three degree gradation of stem changes. Laaha et al. (2011) found a correlation between the degree of transparency and Danish-speaking and German-speaking children’s acquisition rate of plural stems – high transparency correlated with early acquisition of the stem change and lower transparency correlated with later acquisition.
Predictability
Predictability concerns the degree to which a specific plural form may be predicted based on the phonological, semantic, and structural features of its singular stem (e.g., Laaha & Dressler, 2012).
Productivity
Productivity concerns the extent to which a morpheme can be extended to foreign words, neologisms etc. (e.g., Dressler, 2003; Kjærbæk, 2013, 2015; Kjærbæk, dePont Christensen, & Basbøll, 2014).
The acquisition of the Danish noun plural system is interesting when testing the five frequency theses above: whereas for example English is characterized by having one default inflectional marker for a grammatical category (e.g., the plural suffix -s) and a minor number of exceptions to this default rule, Danish has several competing inflectional markers, and there are important interactions between phonology and morphology in the Danish system.
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The Danish noun plural system
In Danish noun plural can be formed in four different ways, namely by:
a) adding a plural suffix to the singular stem as in bil [biːʔl] ‘car’ – bil-er [ˡbiːʔlɐ] ‘cars’
Possible suffixes: /ɐ/, /ə/, /Ø/ and the foreign suffixes /s/, /a/, /i/
b) stem change as in mand [manʔ] ‘man’ – mænd [mɛnʔ] ‘men’
c) adding a plural suffix to the singular stem combined with stem change as in fod [foðʔ] ‘foot’ – fødd-er [ˡføðʔɐ] ‘feet’
Possible stem changes: stød addition, stød drop, syncope, a-quality change, r- insertion, n-insertion and umlaut
d) no change (plural = singular) as in mus [muːʔs] ‘mouse’ – mus [muːʔs] ‘mice’
The Danish plural markers
Based on detailed analyses of the Danish noun plural system from a phonological perspective Basbøll et al. (2011) identified 23 different plural markers (suffix + stem change (incl. no change)). These plural markers are different from markers based on orthography.
Transparency scales
We here present a transparency scale for the Danish plural markers (stem + suffix). First we have developed a scale for the plural stems saying that a plural stem is:
1) Transparent when it equals the singular stem
No stem change (No Change)
bil [biːʔl] ‘car’ – biler [ˈbiːʔlɐ] ‘cars’
2) Partly transparent when it involves prosodic stem change
Stød drop, stød addition, syncope, a-quality/vowel length change (Prosodic Change)
bord [boɐʔ] ‘table’ – borde [ˈboːɐ] ‘tables’
baby [ˈbɛjbi] ’baby’ – babyer [ˈbɛjbiːʔɐ] ‘babies’
gaffel [ˈgɑfəl]/[ˈgɑfl ] ‘fork’ – gafler [ˈgɑflɐ] ‘forks’
blad [blað] ‘leaf’ – blade [ˈblæːðə]/[ˈblæːð ] ‘leafs’
3) Not transparent when it involves phonemic stem change
Umlaut, r-insertion, n-insertion (Phonemic Change)
mand [manʔ] ‘man’ – mænd [mɛnʔ] ‘men’
søster [ˈsøsdɐ] ‘sister’ – søstre [ˈsøsdʁɐ] ‘sisters’
øje [ˈʌjə] ‘eye’ – øjne [ˈʌjnə] ‘eyes’
The three degrees of transparency equals the three degrees of stem change presented in Basbøll et al.
(2011) and Laaha et al. (2011).
We have, furthermore, developed a transparency scale for the Danish plural suffixes, saying that a plural suffix is:
1) Transparent when a suffix is simply added to the stem
/ɐ/-suffix
bil [biːʔl] ‘car’ – biler [ˈbiːʔlɐ] ‘cars’
2) Partly transparent when it is often reduced or assimilated with the stem
/ə/-suffix
hus [huːʔs] ‘house’ – huse [ˈhuːsə]/[ˈhuːːs] ‘houses’
3) Not transparent when it is phonologically non-existing
Ø-suffix
mål [mɔːʔl] ‘goal’ – mål [mɔːʔl] ‘goals’
mand [manʔ] ‘man’ – mænd [mɛnʔ] ‘men’
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On the basis of the stem transparency scale and the suffix transparency scales above, we have developed a transparency scale for the whole plural marker where we combine the information of stem and suffix. When ranking the plural markers with respect to transparency versus opacity, we have considered Prosodic Change to subtract only little from transparency, resulting in the following four-step gradation (of Partly transparent) between Transparent and Not transparent:
1) Transparent when both the plural suffix and the plural stem are Transparent
/ɐ/-suffix + No Change
bil [biːʔl] ‘car’ – biler [ˈbiːʔlɐ] ‘cars’
2) Partly transparent 1 when the plural suffix is Transparent and the plural stem is Partly transparent
/ɐ/-suffix + Prosodic Change
bord [boɐʔ] ‘table’ – borde [ˈboːɐ] ‘tables’
baby [ˈbɛjbi] ’baby’ – babyer [ˈbɛjbiːʔɐ] ‘babies’
sofa [ˈsoːfa] ‘sofa’ – sofaer [ˈsoːfæːʔɐ] ‘sofas’
gaffel [ˈgɑfəl]/[ˈgɑfl ] ‘fork’ – gafler [ˈgɑflɐ] ‘forks’
3) Partly transparent 2 when the plural suffix is Partly transparent and the plural stem is Transparent
/ə/-suffix + No Change
digt [degd] ‘poem’ – digte [ˈdegdə] ‘poems’
tov [tʌw] ‘rope’ – tove [ˈtʌwə]/[ˈtʌww ] ‘ropes’
4) Partly transparent 3 when the plural suffix and the plural stem are both Partly transparent
/ə/-suffix + Prosodic Change
hus [huːʔs] ‘house’ – huse [ˈhuːsə]/[ˈhuːːs] ‘houses’
blad [blað] ‘leaf’ – blade [ˈblæːðə]/[ˈblæːð ] ‘leafs’
5) Partly transparent 4 when the plural suffix is Transparent and the plural stem is Not transparent
/ɐ/-suffix + Phonemic Change
bror [bʁoɐ ] ‘brother’ – brødre [ˈbʁœðʁɐ] ‘brothers’
6) Not transparent when both the plural suffix and the plural stem are Not transparent
Ø-suffix + Phonemic Change
mand [manʔ] ‘man’ – mænd [mɛnʔ] ‘men’
søster [ˈsøsdɐ] ‘sister’ – søstre [ˈsøsdʁɐ] ‘sisters’
øje [ˈʌjə] ‘eye’ – øjne [ˈʌjnə] ‘eyes’
We predict the acquisition to go from Transparent > Partly transparent > Not transparent. We furthermore predict the error direction to go from Not transparent > Partly transparent > Not transparent.
Noun plurals with insertion of /r/ as in søster [ˈsøsdɐ] ‘sister’ – søstre [ˈsøsdʁɐ] ‘sisters’ and /n/ as in øje [ˈʌjə] ‘eye’ - øjne [ˈʌjnə] ‘eyes’, have two possible analyses according to the principles we adopt:
they can be considered as having a non-null plural suffix, i.e. /ɐ/-suffix and /ə/-suffix, respectively, combined with the phonemic stem change and syncope; this analysis is used in Laaha et al. (2011). Or they can be considered as having a Ø-suffix, and then the segmental stem change (insertion of /r/ or /n/) will be the only overt plural marker; this is the analysis chosen in the present paper (as in Basbøll et al., 2011; Kjærbæk 2015; Kjærbæk et al., 2014).
Productivity scale
Kjærbæk et al. (2014) presented a scale with three degrees of productivity. Productivity is here defined as the ability of the inflectional marker to occur on new words. For the plural system this means the ability to add the plural marker to a new singular noun in order to form a new plural noun.
The productivity scale for the Danish plural markers is:
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1) Fully Productive plural markers are plural markers taking the /ɐ/-suffix without phonemic stem change.
2) Semi-productive plural markers are plural markers taking the /ə/-suffix or Ø-suffix, in both cases without phonemic stem change.
3) Unproductive plural markers are plural markers with phonemic stem change (as well as plural markers with the foreign plural suffixes /s/, /a/ and /i/).
In this study we will test the five theses on frequency effects suggested by Ambridge et al. (2015) in a phonological perspective and explore the impact of phonology on morphology. This we will do in three types of empirical data from children acquiring Danish as their first language.
Empirical data Naturalistic data
The naturalistic data consist of spontaneous child language input and output from:
a) the Odense Twin Corpus (OTC) (Basbøll et al., 2002). The subpart used here consists of data from two twin pairs: i) the girls Ingrid and Sara between the ages of 0;10 and 2;7; ii) the girl Cecilie and the boy Albert between the ages of 0;11 and 2;5
b) the Danish Plunkett Corpus (DPC) (Plunkett, 1985; 1986) which consists of data from two singletons: i) the girl Anne between the ages of 1;1 and 2;11; ii) the boy Jens between the ages of 1;0 and 3;11.
The corpus consists of video and audio recordings of children interacting with their families in naturalistic settings (playing and dining situations) in their own home. The input is a mixture of child directed and adult directed speech, though the child is always present. The data are transcribed orthographically using the Child Language Data Exchange System (CHILDES) (MacWhinney, 2000a, b) and coded morphologically and phonologically (according to the standard pronunciation) in OLAM (Madsen, Basbøll, & Lambertsen, 2002). See Kjærbæk (2013) for a detailed description of the naturalistic data.
Table 1 shows the size of the corpus in raw numbers with regard to word tokens and word types (different lemmas) as well as noun tokens and noun types.
Table 1. Sample size of naturalistic spontaneous child language input and output
Words Nouns
Tokens Types Tokens Types
Input 180,360 3,342 14,126 1,574
Output 40,987 1,399 5,743 607
Semi-naturalistic data
The semi-naturalistic data consist of structured interviews focusing on familiar routines. An investigator showed the child five pictures of, for example, a trip to the zoo and a birthday party while asking the child prepared questions for maximal elicitation of plural nouns (e.g., Hvad ser du når du går i zoologisk have? ‘What do you see when you go to the zoo?’). All recordings are transcribed ortographically in CHILDES and coded morphologically and phonologically (according to the standard pronunciation) in OLAM. All nouns are furthermore transcribed phonetically according to the child’s actual pronunciation.
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80 monolingual Danish children (41 girls, 39 boys) in the age groups 3, 5, 7 and 9 years participated in this task, 20 children in each group. Children participating in the interviews also participated in the experiment (see just below).
Experimental data
The experimental data consist of data from a picture based elicitation task inspired by Jean Berko’s study on both real words and pseudo-words (Berko, 1958). This experiment is only based on real words. The test material consists of 48 stimulus items. Only itmes with an overt plural marker were included in the test, i.e. Pure Zeroes (i.e. plural = singular, e.g., mål [mɔːʔl] ‘goal’ - mål [mɔːʔl]
‘goals’) were excluded because of the difficulty of distinguishing Pure Zero production from repetition of the singular form in the plural elicitation task. Since the plural suffixes /s/, /a/ and /i/ are very rare in child language, they were not included in the experiment.
Children were tested orally and individually. Each child was presented with a picture of an object whose name is a singular noun (e.g., bil ‘car’), and the investigator said: Her er en bil ‘Here is a car’.
Then a second picture, of two instances of the same object, was shown to the child, and the investigator asked: Her er to hvad? ‘Here are two what?’, and the child’s task was to provide the respective plural form. Test items were presented in different orders and were preceded by three training items.
160 monolingual Danish children between the ages of 3-10 years participated in the experiment.
Results
The results of the study are presented here.
Input frequency of the plural suffixes
Table 2 shows the input frequency of the Danish plural suffixes in our corpus of naturalistic child language input and output. We see that 64 % of the nouns (type frequency) take the /ɐ/-suffix, 20 % take the Ø-suffix whereas only 12% take the /ə/-suffix. The plural suffixes /s/, /a/, /i/ and nouns with only a plural form are excluded from the table – they sum up to a total of 4 %.
Table 2. Input frequency of the Danish plural suffixes
Suffix Token Type
/ɐ/ 55 % 64 %
Ø 31 % 20 %
/ə/ 10 % 12 %
Total 96 % 96 %
Correctly produced plural suffixes in the experiment
Figure 1 illustrates the proportion of correctly produced plural suffixes by age in the experiment. We see that the proportion of correctly produced plural suffixes increases with age. The /ɐ/-suffix constitutes the highest proportion of correctly produced plural suffixes followed rather closely by the /ə/-suffix, in fact they appear to coincide from the age of six. The proportion of correctly produced Ø- suffixes is rather low, compared to the other two suffixes. Please note that the only zero-plurals included in the experiment have phonemic stem change, that is, Pure Zeros (plural = singular) are not included.
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Figure 1. Proportion of correctly produced plural suffixes by age and type of suffix in the experiment (Kjærbæk, dePont Christensen, & Basbøll, 2014, p. 62)
Input frequency of the plural stem changes
Table 3 shows the input frequency of the Danish plural stem changes (including No change) in our corpus of naturalistic child language input. Please note that a plural form can have more than one kind of stem change at the same time. We see that 71 % (type frequency) of the Danish nouns have No change of the plural stem compared to the singular stem. 14 % have Stød drop, 5 % have Stød addition, 4 % have Umlaut, 2 % have Syncope, 1 % have r-insertion, 0.6 % have a-quality change combined with change in vowel length and only 0.2 % have n-insertion (only one noun, namely øje [ˈʌjə] ‘eye’ – øjne [ˈʌjnə] ‘eyes’).
Table 3. Input frequency of the plural stem changes (including No change)
Stem change Tokens Types
No change 63 % 71 %
Stød drop 15 % 14 %
Stød addition 3 % 5 %
Umlaut 12 % 4 %
Syncope 1 % 2 %
r-insertion 4 % 1 %
a-quality change 0.2 % 0.6 %
n-insertion 2 % 0.2 %
Correctly produced plural stem changes in the experiment
Figure 2 illustrates the proportion of correctly produced plural stem changes by age and type of stem change in the experiment. The highest proportion we find with No change where the children only produce very few errors in all age groups. For all other stem changes we see that the proportion of correctly produced stem changes increases with age. It appears that the correctly produced plural stems fall into three categories:
1) No change
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2) Syncope, a-quality change combined with change in vowel length, Stød drop and Stød addition (these are all prosodic stem changes)
3) Umlaut, r-insertion and n-insertion (which are all phonemic stem changes)
Figure 2. Proportion of correctly produced plural stem changes by age and type of stem change in the experiment (Kjærbæk, dePont Christensen, & Basbøll, 2014, p. 63)
Figure 3 illustrates the proportion of correctly produced plural stems by age and degree of stem transparency in the experiment. Again we see that the children produce very few errors in the No Change category (Transparent), followed by Prosodic Change (Partly transparent) and least correct in the Phonemic Change category (Not transparent).
Figure 3. Proportion of correctly produced plural stems by age and degree of stem transparency in the experiment (Kjærbæk, dePont Christensen, & Basbøll, 2014, p. 64)
Input frequency of the plural marker
Table 4 shows the input frequency of the Danish plural markers in our corpus of naturalistic child language input. The plural markers are here divided according to their degree of productivity. We see that Fully Productive plural markers have an input frequency of 63 % (type frequency), Semi- productive 31% and Unproductive plural markers only have an input frequency of 6 %.